Photographic processes using silver halide have been most widely used in the past due to their excellent photographic properties such as sensitivity or control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques cable of easily and quickly obtaining images have been developed by changing the conventional wet process using a developing solution into a dry development process such as a process using heat, etc.
Heat-developable light-sensitive materials are known in the field of these techniques. Heat- developable light-sensitive materials and processes therefor have been described, for example, in U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, No. 17029, pages 9 to 15 (June, 1978).
Many different processes for obtaining color images have been proposed. With respect to processes for forming color images by the coupling of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, pages 31 and 32 (September, 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Further, a process in which a diffusible dye is released upon the coupling of an oxidation product of a developing agent with a coupler is described in Japanese Patent Application (OPI) No. 79247/83, etc.
However, such developing agents which are employed in these known heat-developable color light-sensitive materials, for example, p-phenylenediamines or p-aminophenols are inferior in their preservability and cause remarkable coloration in non-image areas. On the other hand, p-sulfonamidophenols have a poor silver developing property and coupling property and can not provide color images of high density, although they have improved preservability.
Moreover, hydrazone derivatives as described in Research Disclosure, No. 19417 (June, 1980) have a poor coupling property and can only provide color images of low density. Furthermore, sulfamic acid salts as described in Japanese Patent Application (OPI) No. 146133/81, urea derivatives as described in U.S. Pat. No. 4,426,441, or urea derivatives as described in Japanese Patent Application (OPI) No. 53831/84, etc. are compounds in which p-phenylenediamines or p-aminophenols are stabilized by means of protective groups. However, these compounds also have a poor silver developing property and only provide color images of low density.